During the implantation of a glenoid component of a shoulder prosthesis, the surgeon must prepare the glenoid of the patient in order to bear and immobilize the glenoid component of the shoulder prosthesis. To that end, the surgeon generally uses a motorized or manual milling machine. The milling machine comprises a burr whose proximal side is secured to a driving grip. The distal surface of the burr has reliefs, such as teeth, blades, and/or tips. The burr rotates or oscillates around its central axis in order to shave the bone material making up the glenoid and hollow, cut into, and/or grate the bone material until the glenoid is given a shape adapted to the prosthetic glenoid component to be implanted. For example, the burr hollows a bowl-shaped cavity in the glenoid in which a dedicated portion of the prosthetic glenoid component is housed in a substantially complementary manner. The bowl-shaped cavity may be a hemisphere or another concave cavity.
Furthermore, one potentially significant parameter for lasting stability of a prosthetic glenoid component relates to the proper positioning of that component on the glenoid. Thus, during surgical operations aiming to implant a glenoid component, an orthopedic guide pin, which may be a rod, is pushed partially into the glenoid at a predetermined point and in a predetermined direction. In that manner, the longitudinal part of said rod protrudes from the glenoid and may be used by the surgeon to guide and manipulate different ancillaries. For example, particular bone preparation ancillaries for the glenoid are axially engaged around the guide pin and then slid along said pin.
In particular, the surgeon has milling machines, like those mentioned above, in which the burr includes a hub with a central through bore that is dimensioned to axially receive the guide pin. During a surgical operation, after having placed the guide pin, the surgeon axially slips the proximal end of the pin into the central bore of the burr and then slides said burr and its proximal sleeve along the guide pin towards the glenoid until the distal surface of the burr is pressed against the glenoid. Burrs with a central hub may also be referred to as “cannulated burrs.” By rotating or oscillating the burr around the guide pin, the glenoid is milled precisely, in that the milling is well positioned relative to the glenoid due to the cooperation between the central hub of the burr and the guide pin.
However, the use of cannulated burrs poses implementation difficulties related to the presence of soft tissues around the glenoid as well as the proximity of the humeral head of the operated patient. It is therefore often necessary to place spacers to widely expose the glenoid in order to bring the glenoid longitudinally closer to the pin and avoid interference between the soft tissues and the burrs slid along the guide pin towards the glenoid. It is also often necessary to greatly displace the humeral head, or even resect the humeral head. In some cases, this procedure has the possibility of resulting in trauma and scars that may be significant for the patient.